Sensor Clock Blanking for Common-Mode Transition Rejection
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Solution Overview
Problem
Current sensor integrated circuits face challenges in accurately measuring current through motor windings due to large common mode voltages, which can swing beyond the supply voltage range, causing electrical isolation issues and complicating sensing operations.
Innovation Solution
The integration of an analog front end with a clock signal that has blanking time periods during which the clock signal is held at a constant level, preventing operational interference during common mode input voltage transitions, along with a biasing system that sets the analog front end and tub to a voltage greater than the common mode voltage, and a charging circuit to maintain power and isolate voltage fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If in-line current sensing is used to measure current through motor windings, then current measurement capability is achieved, but the circuitry is exposed to large common mode voltages that swing beyond supply voltage range, causing electrical isolation issues
Solution Approach 1:
The patent introduces an intermediary isolation mechanism between the sense circuitry and the high common mode voltage environment. The sensor IC electrically isolates the sense resistor from the motor winding common mode voltage while still allowing accurate current measurement through the sense resistor, thus protecting the circuitry from harmful voltages without sacrificing measurement capability
Solution Approach 2:
The patent changes the electrical parameters of the sensing system by introducing isolated measurement paths and differential signaling that can operate independently of the common mode voltage level. This allows the sense circuitry to measure current accurately while the common mode voltage swings beyond the supply voltage range without affecting the measurement
2Object-affected harmful factors
If multi-chip solution is used to electrically isolate sense circuitry from large common mode voltages, then electrical isolation is achieved, but device complexity increases
Solution Approach 1:
The patent merges the isolation function with the current sensing function into a single integrated sensor IC. Instead of using separate multi-chip configurations, the sensor IC combines the sense resistor, isolation circuitry, and measurement electronics into one unified device, thereby achieving electrical isolation without increasing device complexity
Solution Approach 2:
The sensor IC performs multiple functions within a single device: it provides electrical isolation from common mode voltage, measures current through the sense resistor, and outputs the measurement signal. This multi-functional approach eliminates the need for separate isolation chips and sensing circuits, reducing overall system complexity
3Productivity
If clock signal operates continuously during common mode input voltage transitions, then productivity is maintained, but measurement precision deteriorates due to transitions affecting the clock signal
Solution Approach 1:
The patent implements periodic sampling of the sense resistor voltage at controlled intervals, rather than continuous operation. The clock signal is synchronized with the motor controller's switching cycle, and measurements are taken at specific phases when common mode voltage transitions are minimal, thereby maintaining measurement precision while achieving effective continuous monitoring through periodic updates
Data Source
AI summary
A sensor includes an analog front end having a circuit element responsive to a clock signal and a clock generating circuit configured to generate the clock signal having blanking time periods during which the clock signal is held at a constant level, wherein the circuit element is not operational during the blanking time periods. The blanking time periods correspond to time periods during which transitions of a common mode input voltage to the sensor are expected to occur.